Grade 11
  1. Basic concepts of chemistry  1.1. Importance of Chemistry  1.2. Nature and scope of chemistry  1.3. laws of chemical combination  1.3.1. Law of conservation of mass  1.3.2. Law of definite proportions  1.3.3. Law of multiple proportions  1.3.4. Law of gaseous volume  1.3.5. Avogadro's Law  1.4. Dalton's atomic theory  1.5. Mole concept and molar mass  1.6. Percent composition  1.7. Empirical and molecular formula  1.8. Stoichiometry and Stoichiometric Calculations  1.9. Limiting reagent concept
  2. Structure of the atom  2.1. Discovery of the electron, proton, and neutron  2.2. Atomic Model  2.2.1. Thomson's model  2.2.2. Rutherford's model  2.2.3. Bohr's model  2.3. Quantum mechanical model of the atom  2.4. Dual nature of matter and radiation  2.5. Heisenberg's uncertainty principle  2.6. Quantum numbers  2.7. Atomic orbitals and their shapes  2.8. Electronic configuration of elements  2.9. Aufbau principle  2.10. Pauli's exclusion principle  2.11. Hund's maximum multiplicity rule  2.12. de Broglie's hypothesis  2.13. Photoelectric effect
  3. Classification of elements and periodicity in properties  3.1. Historical development of the periodic table  3.2. Modern Periodic Law and Periodic Table  3.3. Periodic trends in properties  3.3.1. Atomic and Ionic Radius  3.3.2. Ionization enthalpy  3.3.3. Electron gain enthalpy  3.3.4. Electronegativity  3.3.5. Valency  3.3.6. Metallic and Non-Metallic Properties  3.3.7. Oxidation states  3.4. Unusual Properties of the First Elements
  4. Chemical Bonding and Molecular Structure  4.1. Kossel–Lewis approach to chemical bonding  4.2. Ionic or electrovalent bond  4.3. Covalent bond and its features  4.4. Bond parameters  4.5. VSEPR Theory  4.6. Valence bond theory  4.7. Hybridization and its types  4.8. Molecular orbital theory  4.8.1. Bond order and stability  4.9. Hydrogen bonding
  5. States of matter  5.1. Intermolecular forces  5.2. Gas Laws  5.2.1. Boyle's law  5.2.2. Charles's Law  5.2.3. Avogadro's Law  5.2.4. Dalton's law of partial pressure  5.2.5. Graham's law of spread  5.3. Ideal Gas Equation and Applications  5.4. Real gases and deviations from ideal behaviour  5.5. Kinetic molecular theory of gases  5.6. Liquefaction of gases  5.7. Properties of Liquids  5.8. Surface tension and viscosity
  6. Thermodynamics  6.1. System and environment  6.2. Types of systems in thermodynamics  6.3. Types of procedures  6.4. First law of thermodynamics  6.5. Internal energy and enthalpy  6.6. Heat capacity and specific heat  6.7. Hess's law of constant heat summation  6.8. Bond dissociation enthalpy  6.9. Enthalpy of formation and combustion  6.10. Enthalpy of solution and neutralization  6.11. Spontaneity and the second law of thermodynamics  6.12. Gibbs free energy and its applications
  7. Balance  7.1. The concept of balance  7.2. Equilibrium constant and its applications  7.3. Le Chatelier's principle  7.4. Ionic equilibrium in solutions  7.5. Acid and Base Theory  7.5.1. Arrhenius concept  7.5.2. Bronsted-Lowry concept  7.5.3. Lewis concept  7.6. pH Scale and pOH  7.7. Common ion effect  7.8. Hydrolysis of salts  7.9. Buffer solutions and their mechanism of action  7.10. Solubility equilibrium of sparingly soluble salts
  8. Redox reactions  8.1. Oxidation and reduction concepts  8.2. Oxidation number and its applications  8.3. Redox reactions in terms of electron transfer  8.4. Balancing redox reactions (oxidation number and ion-electron methods)  8.5. Types of redox reactions  8.6. Electrochemical Cells and Redox Reactions
  9. Hydrogen  9.1. Position of Hydrogen in the Periodic Table  9.2. Isotopes of hydrogen  9.3. Preparation of Hydrogen  9.4. Properties of Hydrogen  9.5. Hydrides and their classification  9.6. Water and heavy water  9.7. Hydrogen peroxide and its properties  9.8. Uses of Hydrogen and Its Compounds
  10. S-block elements (alkali and alkaline earth metals)  10.1. Group 1 Elements - Properties and Trends  10.2. Group 2 Elements - Properties and Trends  10.3. Unusual properties of lithium and beryllium  10.4. Important compounds of sodium and their uses  10.5. Important Compounds of Magnesium and Calcium
  11. Some p-block elements  11.1. General Introduction to p-Block Elements  11.2. Group 13 Elements  11.2.1. Boron and its compounds  11.3. Group 14 Elements  11.3.1. Carbon and its allotropes  11.3.2. Important Compounds of Carbon and Silicon
  12. Organic Chemistry - Some Basic Principles and Techniques  12.1. Classification and Nomenclature of Organic Compounds  12.2. Structural representation of organic compounds  12.3. Classification of organic reactions  12.4. Electronic Effects in Organic Chemistry  12.4.1. Inductive effect  12.4.2. Resonance effect  12.4.3. Hyperconjugation  12.5. Reaction mechanism and intermediate species  12.6. Purification and qualitative analysis of organic compounds
  13. Hydrocarbons  13.1. Hydrocarbons  13.1.1. Preparation and Properties of Alkenes  13.2. alkene  13.2.1. Preparation and Properties of Alkenes  13.2.2. Electrophilic addition reactions  13.3. Alkynes  13.3.1. Preparation and Properties of Alkynes  13.4. Aromatic hydrocarbons  13.4.1. Structure and properties of benzene  13.4.2. Electrophilic substitution reactions of benzene
  14. Environmental Chemistry  14.1. Environmental Pollution  14.2. Atmospheric pollution and the greenhouse effect  14.3. Water pollution and treatment methods  14.4. Soil pollution and its effects  14.5. Industrial waste and its treatment  14.6. Strategies for pollution control

Grade 11 → Basic concepts of chemistry ↓


Percent composition


Percent composition is an important concept in chemistry that helps us understand the elemental makeup of compounds. It's a way of expressing the relative amounts of each element in a compound, which can be useful for a variety of applications, such as determining the purity of a substance or understanding its molecular structure.

Basics of percentage composition

In chemistry, when we talk about compounds, we mean a substance that is formed when two or more elements are chemically bonded together. Each compound has a unique chemical formula that tells us the type and number of atoms present. To understand these compositions quantitatively, we use something called percent composition.

The percent composition of a compound is the percentage by mass of each element in the compound. It is calculated using the formula:

Percentage of element X = (mass of X in the compound / molar mass of the compound) × 100

Where:

  • The mass of X is the total mass of the element X in a given amount of the compound.
  • The molar mass of a compound is the sum of the masses of all the atoms present in one mole of the compound.

Calculating percent composition

To find the percent composition of a compound, follow these steps:

  1. Determine the molar mass of each element in the compound.
  2. Calculate the total molar mass of the compound.
  3. Divide the molar mass of each element by the total molar mass of the compound and multiply by 100 to get the percentage.

Example: Percentage composition of water (H2O)

Water is composed of hydrogen and oxygen. The formula for water is H2O, which indicates two hydrogen atoms and one oxygen atom.

  • The molar mass of hydrogen (H) is about 1 g/mol.
  • The molar mass of oxygen (O) is about 16 g/mol.

First, calculate the total molar mass of water:

Total molar mass of H2O = (2 × 1 g/mol) + 16 g/mol = 18 g/mol

Next, calculate the percentage composition:

Percentage of Hydrogen:

(2 g/mol / 18 g/mol) × 100 = 11.11%

Percentage of Oxygen:

(16 g/mol / 18 g/mol) × 100 = 88.89%

Thus, water contains about 11.11% hydrogen and 88.89% oxygen by mass.

Visual example

Let's visually understand how percent composition works by using a simple example for a binary compound such as sodium chloride (NaCl):

Sodium (Na) Chlorine (Cl) Na Cl 39.34% 60.66%

In this example, by calculating the molar mass of sodium chloride and applying the percent composition formula, we find that the compound contains 39.34% sodium and 60.66% chlorine by mass.

Another example: Calculating the percentage composition of glucose (C6H12O6)

Glucose is a simple sugar with the formula C6H12O6. Let's determine its percentage composition:

  • Molar mass of carbon (C) = 12 g/mol
  • Molar mass of hydrogen (H) = 1 g/mol
  • Molar mass of oxygen (O) = 16 g/mol

Calculate the total molar mass of glucose:

Total molar mass of C6H12O6 = (6 × 12 g/mol) + (12 × 1 g/mol) + (6 × 16 g/mol) = 180 g/mol

Now, calculate the percentage of each element:

Percentage of Carbon:

(72 g/mol / 180 g/mol) × 100 = 40%

Percentage of Hydrogen:

(12 g/mol / 180 g/mol) × 100 = 6.67%

Percentage of Oxygen:

(96 g/mol / 180 g/mol) × 100 = 53.33%

Summary

Therefore, glucose contains 40% carbon by mass, 6.67% hydrogen by mass, and 53.33% oxygen by mass. Understanding these compositions is helpful in a variety of scientific disciplines and applications.

Applications of percent composition

Percent composition is a fundamental concept that has various applications in chemistry and related fields, including:

  1. Formulating chemical reactions: Knowing the percent composition helps balance equations and predict the amounts of reactant and product in chemical reactions.
  2. Analysis of chemical purity: This helps determine the purity of a substance, which is important in industrial applications and research.
  3. Develop nutritional information: Food chemistry relies on percent composition to create nutritional labels and ensure food quality.
  4. Environmental chemistry: Understanding the percentage composition of elements in pollutants helps in assessing their impact and planning mitigation strategies.

Exercises for practice

Here are some exercises to help you solidify your understanding of percent composition. Calculate the percent composition for the given compounds:

  1. CO2 (carbon dioxide)
  2. NH4Cl (ammonium chloride)
  3. CaCO3 (calcium carbonate)

Conclusion

Percent composition is an important concept that allows us to understand more about the substances that make up the world around us. By calculating the mass of each element in a compound, we obtain information that is vital for a wide range of chemical applications. By mastering this calculation, chemists can accurately describe compounds, analyze their properties, and apply this knowledge to a variety of scientific discoveries.


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Percent composition

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